The poll, by Reuters News Agency and Ipsos market research company, shows Republican presidential candidate Trump's support has increased since rivals Ted Cruz and John Kasich exited the race.
In the span of one week, Trump's support increased to 40%, just one percent less than Hillary Clinton's 41%. Some 19% of voters are still undecided. A week ago Clinton led Trump by as much as 13%.
It's six months before the elections and the competition is likely to stiffen, as another Reuters/Ipsos poll found earlier that the majority of voters don't trust either candidate with responsibilities such as managing the US economy, fulfilling duties as commander in chief, and conducting themselves according to a "high moral standard."
The most recent poll was conducted between May 6 and 10 and surveyed 1,289 likely voters online. The margin of error was 3 percentage points.
